[Milsurplus] [armyradios] Re: [vmars] Re: [ham-hist] Fox-hole radios

[Robert Nickels]

On 7/7/2010 8:45 AM, J. Forster wrote:
>
> some years ago there was a thread on another Group about the 
> properties of a Razor Blade detector
>
Back in my yout' I build many of them and the foxhole radio got me 
through several grade school science fairs ;-)  Mine were based on an 
article from Popular Mechanics (or Science?) that used a bent safety pin 
as the catwhisker, but with a piece of pencil lead wired to the end to 
actually contact the razor blade.  They said a blade with some rust 
would probably work better, and you'd have to probe around to find a 
sensitive spot.   They worked as well as my storebought "Remco" crystal 
set, which is to say, you could hear the local BC station but not much else.

> IMO, a comparison between a Razor Blade and a Galena "Cat's Whister" 
> (ie point contact diode) detector would be very interesting indeed.
>
A few years ago I became interested in early solid state and especially 
negative resistance devices, which led me to the fascinating website of 
my pal Nyle Steiner K7NS:     http://home.earthlink.net/~lenyr/         
He's put several photos of the waveform and V/I curve on his negative 
resistance pages that will give you some idea of how well these devices 
perform.

I was able to adapt Nyle's oscillator concept to create a crystal 
controlled RF oscillator using a piece of oxidized galvanized sheet 
metal that could be keyed and even amplitude modulated.   We've been 
able to copy the microwatt-level signal from these simple transmitters 
up to several miles away.  Our experiments with this type of oscillator 
can be found at his new website:  http://www.sparkbangbuzz.com/

I've had many questions after I put up a little Youtube video:  
http://www.youtube.com/watch?v=cDBpBYkRw0Q
  but this is more of a novelty than a practical way to communicate.  
Finding a spot that provides the right characteristics to sustain 
oscillation at RF frequencies is painstaking and if you bump the table 
you'll probably go off the air!   But making an RF signal using "junk" 
without an active tube or semiconductor is quite a thrill, and I've 
fantasized about how an military radio op behind enemy lines might have 
put this idea to use, had he known about it.

73, Bob W9RAN